The present invention relates to a cord drive which can be used for opening and closing or tilting coverings for architectural openings such as Venetian blinds, pleated shades, vertical blinds, other expandable materials, and other mechanical devices.
Typically, a blind transport system will have a head rail which both supports the blind and hides the mechanisms used to raise and lower or open and close the blind. Such a blind system is described in U.S. Pat. No. 6,536,503, Modular Transport System for Coverings for Architectural Openings, which is hereby incorporated herein by reference. In the typical top/down product, the raising and lowering of the blind is done by a lift cord or lift cords suspended from the head rail and attached to the bottom rail (also referred to as the moving rail or bottom slat). The opening and closing of the blind is typically accomplished with ladder tapes (and/or tilt cables) which run along the front and back of the stack of slats. The lift cords usually run along the front and back of the stack of slats or through holes in the middle of the slats. In these types of blinds, the force required to raise the blind is at a minimum when the blind is fully lowered (fully extended), since the weight of the slats is supported by the ladder tape so that only the bottom rail is being raised at the onset. As the blind is raised further, the slats stack up onto the bottom rail, transferring the weight of the slats from the ladder tape to the lift cords, so progressively greater lifting force is required to raise the blind as the blind approaches the fully raised (fully retracted) position.
Some window covering products are built in the reverse (bottom up), where the moving rail, instead of being at the bottom of the window covering bundle, is at the top of the window covering bundle, between the bundle and the head rail, such that the bundle is normally accumulated at the bottom of the window when the covering is retracted and the moving rail is at the top of the window covering, next to the head rail, when the covering is extended. There are also composite products which are able to do both, to go top down and/or bottom up.
In horizontal window covering products, there is an external force of gravity against which the operator is acting to move the expandable material from one of its expanded and retracted positions to the other.
In contrast to a blind, in a typical top down shade, such as a shear horizontal window shade, the entire light blocking material wraps around a rotator rail as the shade is raised. Therefore, the weight of the shade is transferred to the rotator rail as the shade is raised, and the force required to raise the shade is thus progressively lower as the shade (the light blocking element) approaches the fully raised (fully open) position. Of course, there are also bottom up shades and also composite shades which are able to do both, to go top down and/or bottom up. In the case of a bottom/up shade, the weight of the shade is transferred to the rotator rail as the shade is lowered, mimicking the weight operating pattern of a top/down blind.
In the case of vertically-oriented window coverings, which move from side to side rather than up and down, a first cord is usually used to pull the covering to the retracted position and then a second cord is used to pull the covering to the extended position, since the operator is not acting against gravity. However, these window coverings may also be arranged to have another outside force or load other than gravity, such as a spring, against which the operator would act to move the expandable material from one position to another.
A wide variety of drive mechanisms is known for moving coverings between their extended and retracted positions and for tilting slats. A cord drive to raise or lower the blind is very handy. It does not require a source of electrical power, and the cord may be placed where it is readily accessible, getting around many obstacles.
A single cord may perform both a drive function and a lift function, being pulled by the operator to drive the blind up and down (the drive function), and attaching to the bottom rail to raise and lower the blind (the lift function), so the same cord functions both to drive the blind and to lift the bottom rail. Alternatively, there may be drive cord(s) and lift cords that are totally separate and independent from each other, with the drive cord being pulled to cause a drive spool to rotate, and the rotation of the drive spool driving a lift spool, which then wraps up the lift cord to raise the bottom rail.
Known cord drives have some drawbacks. The cords in a cord drive, for instance, may be hard to reach when the cord is way up (and the blind is in the fully lowered position), or the cord may drag on the floor when the blind is in the fully raised position. The cord drive also may be difficult to use, requiring a large amount of force to be applied by the operator, or requiring complicated changes in direction in order to perform various functions such as locking or unlocking the drive cord. There may also be problems with overwrapping of the cord onto the drive spool, and many of the mechanisms for solving the problem of overwrapping require the cord to be placed onto the drive spool at a single location, which prevents the drive spool from being able to be tapered to provide a mechanical advantage.